According to the research published Tuesday in the Journal of the American Medical Association, "the prevalence of self-reported, past-month marijuana use among United States adult pregnant women increased from 2.4 percent to 3.9 percent".
Overall there was a rise from around 4 percent to around 7 percent, researchers from healthcare consortium, Kaiser Permanente Northern California, found. In 2016, almost a quarter of pregnant teenagers had used marijuana, as had about one in five women between 18 and 24.
With medical marijuana and legal recreational use spreading across the country, it seems as though the movement has extended to moms-to-be, according to a new study.
Study authors said they were concerned about the significant rise of pot use among younger women - in 2016 alone, 22 per cent of the mothers-to-be, age 12 to 18 years, and 19 per cent age 18 to 24 years screened positive for marijuana use.
An analysis of all that data revealed that women across all age groups reported smoking weed while pregnant at higher rates in 2016 than 2009.
Prenatal marijuana use also increased among women of all ages.
Researchers relied on self-administered questionnaires completed by 279,457 women eight weeks into their pregnancy.
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While studies on pregnant women who use marijuana have been limited, the researchers state that prenatal use of marijuana may impair fetal growth and neurodevelopment.
However, the institute says more research must be done to determine which effects are related to marijuana exposure and which are related to environmental factors that could be associated with the mother's marijuana use, such as poverty or other drug use.
Barbara Yankey, a researcher at Georgia State University, told Reuters marijuana use may be on the rise because of the recent legalization of its recreational use "has made people think of the drug as less risky, even during pregnancy".
They also say that "there are insufficient data to evaluate the effects of marijuana use on infants during lactation and breastfeeding, and in the absence of such data, marijuana use is discouraged".
On January 1, 2018, marijuana will become legal for recreational use in California, making it easier to buy for anyone over 21 there.
And women may even be using marijuana after they took the survey-on goal. However, on a federal level, it is still illegal to possess, use, buy, sell, or cultivate marijuana.